Notably, revenues do not reflect total billings since Apple reports only 30% of app transaction values. The 'gross' revenues are now about $7 billion per quarter.
On a yearly basis the iTunes/Software/Services group had gross revenues of $23.5 billion with growth of 34% y/y.
Check out the chart below that compares the iTunes group to Google's core search business. It's nearly half the size and growing slightly faster.